Most people know that go0gle is a valuable tool for searching the Internet. I've discovered recently, though, that most people DON'T know that you can also use it to convert distance, area, and volume; currency; and temperatures. You can also use it to perform mathematical functions, like a calculator.
I found this to be particularly useful for this site, since we have people from around the world who all deal in different measurements. I find it useful, in general, because it works with the way your brain thinks, not with the way computers think.
For example, you can type any of the following into the search field, and go0gle will give you an answer.
4*16 (or 4 times 16)
12^2 (or 12 squared)
sqrt(64) (or square root of 64)
2 feet in inches
2 feet in meters (or metres!)
4800 cubic inches (or in^3) in gallons
1 cup in ml
30 UK gallons in US gallons
12 USD in GBP (us dollars to pounds)
12 dollars in British money (more like how we think)
65 F to C
So go ahead--try it! You'll be surprised at how simple it is.